AJP - Regulatory, Integrative and Comparative Physiology, Vol 261, Issue 6 1461-R1464, Copyright © 1991 by American Physiological Society
Development of passive permeability characteristics of rat placenta during the last third of gestation
D. E. Atkinson, N. R. Robinson and C. P. Sibley
Department of Child Health, The University of Manchester, St. Mary's Hospital, United Kingdom.
To investigate how the passive permeability of the rat placenta changes
during the last third of gestation we measured the unidirectional
maternofetal clearance (Kmf) of three polar nonelectrolytes. We found that
Kmf (microliters.min-1.g placenta-1) for all three tracers increased
between days 15 and 22 (term is 23 days). The increase was less for the
largest tracer, [14C]inulin (3.5-fold increase from 0.5 +/- 0.1 to 1.6 +/-
0.1 microliters.min-1.g placenta-1), than for the smaller tracers,
[14C]mannitol (7-fold increase from 1.6 +/- 0.1 to 10.9 +/- 0.4
microliters.min-1.g placenta-1) and 51Cr-labeled EDTA (9.5-fold increase
from 0.8 +/- 0.04 to 7.6 +/- 0.7 microliters.min-1.g placenta-1). These
data suggest that whilst the overall permeability of the rat placenta
increases during this period of pregnancy, restriction to the diffusion of
large (greater than or equal to 1.5 nm molecular radius) polar
nonelectrolytes also increases.
